1. Field of the Invention
The present invention relates to a semiconductor device, more particularly to a permeable base transistor (PBT).
2. Description of the Related Art
A PBT comprising an emitter layer, comb-shaped or lattice-shaped base electrodes, a base layer, a collector layer, an emitter electrode, and a collector electrode is well known.
In a PBT, the value of the voltage applied to the comb-shaped base electrode can be used to change the coverage of the depletion layer extending from the base electrode in the horizontal direction. This effect can be used to control the electrons which pass between the comb-shaped base electrodes from the emitter layer to the collector layer.
The thickness of the base electrode is about 0.02 .mu.m. This corresponds to a field effect transistor (FET) which has a short channel length of 0.02 .mu.m. Therefore, the base electrons transit time in the PBT is very short, enabling high speed operation.
However, the switching speed of such a PBT is about 15 ps at most. Thus, a higher switching speed PBT is required. To obtain a higher switching speed PBT requires a more complicated structure and special processes.